A metering device having a piston pump is already known from the prior art. Thus, for example, patent specification DE 42 06 576 B4 discloses a method and an arrangement for determining the conveyance quantity or the conveyance stream by a piston pump. The conveyance quantity may then be determined on the basis of the stroke number or the stroke frequency, and also the conveyance volume of the individual pressure strokes.
A method and a device for metering a liquid medium are disclosed by document DE 10 2011 122 268 B3. The appendix discloses a metering device in the form of a piston pump having a cylinder and a displaceable piston. In the disclosed embodiment, the medium flows into the cylinder chamber via an inlet line and the excess medium flows out of the cylinder chamber via a separate outlet line in the piston base. The metered volume flows out of the piston pump via an additional outlet line in the cylinder base. This embodiment represents a very complex design, because at least one inlet line and two outlet lines are required for this purpose.
The arrangement of valves in the piston base is also very complex, since the discharge lines must be implemented as movable hoses, to follow the movements of the piston.
A further disadvantage in this embodiment is that a medium only flows through the inlet line when it is introduced into the cylinder chamber. A standing medium is thus always present in the inlet line, which cools down in this time, for example. A chemical change of the medium can also occur during longer standing times in the inlet line.
A further disadvantage is that the inlet line is very cumbersome to clean or flush, since each flushing operation must be performed through the cylinder chamber. The inlet valve is also situated far away from the cylinder chamber. A certain amount of residual liquid therefore always remain in the last section, which is then possibly flushed into the cylinder chamber.